Jam warning control circuit



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United States Patent 3,341,837 JAM WARNING CONTROL CIRCUIT HaroldWashington, Broadview, lll., assignor to Instrumentation and ControlSystems, Inc., Villa Park, Ill. Filed Feb. 1, 1965, Ser. No. 429,510 12Claims. (Cl. 340-259) ABSTRACT OF THE DISCLOSURE Electronic circuitcontrol, for monitoring and controlling an automatic fed machine todetermine jamming and prevent further use of the machine untilmalfunction is corrected.

This invention relates to control circuits for automatic machines andmore particularly to circuits for controlling automatically fed machineswhen they jam.

One example of such a machine is a laundry combination comprising awasher-dryer coupled to a folder by a conveyor system. The output of thefolder feeds into a stacker. The conveyor might be adapted to sort thewash into various classes and sub-classes. Thus, the laundry classlinens might be divided into the sub-classes white and coloredresponsive to the amount of light reflected from the individual piecesof linen into a photo electric cell.

The control circuit of this invention is designed to monitor the flow oflaundry through the conveyor system. When a machine jams, the laundrypiles up and might become torn. Worse still, expensive machinery mightbe damaged or ruined.

Hence, an object of the invention is to detect the jamming of anautomatic machine before any damage can occur.

Another object is to stop the products feeding into a jammed machine.

Yet another object is to divert the flow of input goods from the jammedmachine into another machine which is not jammed.

These and other objects will become apparent from a study of theattached drawing in which:

The single figure is a schematic diagram showing a jam warning controlcircuit for a conveyor system associated with an automatic machine.

It should be clearly understood, however, that the control circuit ofthis invent-ion is not limited to use with this particular conveyor, orwith any specific Inachine. Quite the contrary, the invention will findutility with many machines. It will also find utility wherever it iseither necessary or desirable to monitor the flow of work pieces and tostop or divert such flow responsive to a congestion of such pieces.

In the drawing, a double, dot-dashed line separates a conveyor systemfrom a jam warning control circuit 11.

The conveyor system 10 comprises a driving source of motive power (suchas motor 15), a number of conveyor belts 16, 17 and 18, and a traflicflow selector 20. To make the showing generic, belt 16 is called aninput and belts 17 and 18 are called outputs. Each of the conveyors 16,17 and 18 is here shown as a belt travelling in a direction indicated byan arrow head. For example, the belt 16 travels in the directionindicated by the arrow head 21.

While the nature of associated machinery is not of essential importanceto the invention, it is here assumed that a washer-dryer combinationdeposits laundry on belt 16. symbolically, this depositation is shown bythe input arrow 22. It is also assumed that this laundry is conveyedthrough either of two folding machines by belts 17, 18 to either of twostackers. The output from the 3,341,837 Patented Sept. 12, 1967 foldingmachines is symbolically represented at 23 and 24.

The trafiic flow selector 20 is shown as a doorlike arrangement 25 whichmay swing to either of two positions under the control of any suitabledevice 26. The device 26 is controlled by a signal from a selector SEL(which could be a photo-electric cell). When the device 26 swings thedoor 25 to the position shown by solid lines, the laundry on conveyor 16follows the path of the solid line arrow 28 to conveyor 18 in a foldingmachine and then to a stacker, at 24. When the device 26 swings the door25 to the position shown by dashed lines, the laundry on conveyor 16follows the path of the dashed line arrow 29 to conveyor 17 in anotherfolding machine and then to a stacker, at 23. The terms class 1 outputand class 2 output are intended as a generic disclosure of any desiredsorting. It could be assumed that the class 1 output on conveyor 17 iswhite linens and the class 2 output on conveyor 18 is colored linens.

Means are provided for monitoring the flow of traflic through theconveyor system. More particularly, one detector 30 provides an outputpulse for each item deposited on conveyor 16 by machine 22. Otherdetectors 31 and 32 provide an output pulse for each item expelled fromthe folding machines to the stackers, as indicated at 23 or 24. It Willbe convenient to refer to the pulses from detector 30 as input pulsesand the pulses from detector 31 or 32 as output pulses.

The input and output pulses have opposite effects. One adds and theother subtracts. As long as the input and output pulses tend to beinterleaved so that opposites follow each other, the net result might bedescribed as effectively centered at zero. However, if the operatingmachine (say, conveyor 17) jams, the number of input pulses exceeds thenumber of output pulses. The cumulative total of the pulses drifts awayfrom zero, and the jam warning circuit 11 commands the conveyor systemto take appropriate action. This action could be to stop the conveyor.Or it could be to divert the flow of laundry by changing the position ofdoor 25.

The jam warning control circuit for accomplishing this functioncomprises a gate circuit 40, a memory circuit 41, a jam detector 42, atimer circuit 43, and an output control circuit 44. The input gatecircuit includes an electronic switch 50, here shown as an NPNtransistor which is normally biased to an off condition by 12 voltsapplied to its base via resistor 51.

When a piece of laundry is fed into the machine, the detector 30provides an input pulse. Then the timer 52 responds and applies a groundpotential to the upper end of resistor 53 for a period of 150milliseconds. The two series connected resistors 51 and 53 divide thevoltage and apply a forward bias potential to the base of transistor 50,which turns on.

When the electronic switch turns on, a 12 volt potential is applied tothe lower end of a voltage divider formed by the two resistors 55 and56. The voltage division is such that a forward bias appears on thecontrol electrode of a constant current generator device, (which is hereshown as including a PNP transistor 57).

Means are provided for remembering the number of pieces of laundry inthe machine at any given time. This the switch 57 turns off, theincremental charge remains stored on the capacitor.

The folding machine will process an average number of pieces of laundryduring any given period of time. However, the number of pieces may varyat any instant as compared with any other instant according to the timerequired to complete the folding of the individual pieces. Therefore, ineffect, the conveyor system 16-18 stores laundry while the foldingmachine is processing it and the detectors may send more input thanoutput pulses. The capacitor 60 thus receives more than one incrementalcharge.

Under normal operation, however, the folder soon completes its cycle andsends a folded piece of laundry to the stacker, as symbolically shown bythe arrows 23 or 24. As the laundry leaves the folder, the detector cuit11. Then, the capacitor 60 is partially discharged. 31 sends an outputpulse to the jam warning control cir- Thereafter, on the average, onepiece of laundry leaves the folding machine every time that anotherpiece of laundry enters it. Thus, the input and output pulses will tendto follow each other. Otherwise, pieces of laundry collect in the folderand it jams.

Assume first that the machine does not jam and a folded piece of laundrypasses out of the folder every time that a piece enters. When thecontacts 31 or 32 close, a timer, such as 65, applies a strong negativepulse (in the order of 24 volts, for this circuit) to an OR gate 66 atthe input of the timer circuit 43.

The timer circuit 43 is shown as a monostable circuit having two activeelements which are a PNP transistor 67 and a unijunction transistor 68.A series of three resistors 69, 70 and 71 form a voltage dividerconnected between 12 and 12 volts, for normally applying a reverse biasto the base of the transistor 67. The resistors 72-75 form a biasnetwork which provides the potentials that normally hold the unijunctiontransistor 68 in an off condition.

When either of the timers 65 or 76 applies a high negative voltage tothe lower end of the resistor 70, the transistor 67 turns on. Thisgenerates a voltage pulse which passes over the circuit from ground G1through the emitter-collector of transistor 67, and capacitor 77 to thebase B2 on the unijunction transistor 68. This pulse reduces the voltagedifference between base B2 and emitter E to turn on the transistor 68.

Before the unijunction transistor 68 turns on, the upper plate ofcapacitor 78 is standing at a potential which is set by the voltagedivider 73, 75. The lower plate is at 12 volts. After the transistor 68turns on, the capacitor 78 discharges into the emitter E for holding theunijunction transistor 68 on for a predetermined period of time. Afterthe capacitor 78 discharges sufficiently, the emitter current reduces,and the transistor 68 turns off. The monostable timer circuit 43 thenreturns to normal with both of the transistors 67 and 68 turned off.

While the transistor 68 is on, a ground pulse is sent over wire 79 andinto the control electrode of an elec tronic switch, here shown as anNPN transistor 80. This pulse makes the base positive relative to theemitter, and the transistor 80 turns on. The emitter and collector ofthe transistor 80 are connected through a current limiting resistor 81to discharge the capacitor 60. The circuit values are selected so thatthe potential which drains olf the capacitor 60 is exactly equal to theincremental charge stored on the capacitor when a piece of laundry tripsthe input detector 30.

It should now be clear how the jam warning control circuit 11 operateswhen there is no jam in the folding machine. Each time that a piece oflaundry enters the folding machine, detector 30 sends an input signaland an incremental charge is stored on the capacitor 60. Each time thata piece of laundry leaves the folding machine contacts 31 or 32 close,and transistor 80 conducts to discharge the capacitor 60 by oneincremental charge.

For any one of many reasons, which are not essential to the invention,it is desirable for the circuit to give a jam warning only after apredetermined number of incremental charges have been stored on thecapacitor 60 with no intervening discharges through the transistor 80.Thus, the circuit values are selected so that the total charge oncapacitor 60 reaches a threshold potential after a predetermined numberof incremental charges are stored. An adjustment of the potentiometer 58selects the exact number of incremental charges required to reach thisthreshold potential. In one machine, this number could be varied fromfour to six.

Means are provided for detecting a jammed condition responsive to thecharge on capacitor 60 reaching the threshold potential. In greaterdetail, the jam detector circuit comprises a silicon controlled switch(SCS) 82 biased to an off condition by the resistors 83a and 83b. A SCSsuch as this will turn on when the voltage at its anode A exceeds thevoltage at its gate G. Thus, the circuit values are selected so that theSCS 82 turns on responsiveto the storage of the threshold potential onthe capacitor 60. The capacitor 84 slows the voltage change across theSCS 82 so that it will not fire on a lower than usual potential owing toits rate sensitivity. Also, the resistor 83a, in series with thecapacitor 84, acts as a filter to pass transients which might otherwiseturn off the SCS 82.

Once the SCS 82 turns on, current flows through the bias resistor 83band a coupling resistor 85 to cause the output control circuit 44 tooperate.

The output control circuit 44 includes a relay connected in parallelwith a spark suppression diode 91 and a current dividing resistor 92.The current through this parallel circuit is manually controlled at apushbutton 95 and automatically controlled by an electronic switch, suchas a silicon controlled rectifier (SCR) 96. The current through resistor92 holds the SCR on after it turns on. A capacitor 97 is connectedacross SCR 96 to slow the rise time of the applied firing voltage andpass transients.

The operation of the output control circuit 44 begins when the SCS 81turns on to apply a voltage through the resistor 85. This turns on theSCR 96. When the SCR conducts, current divides between the relay 90 andthe resistor 92. The current through resistor 92 latches the SCR 96 inits on condition unti-l pushbutton 95 is pushed.

The relay 90 operates. At contacts 96, it opens a circu t to prevent thenormal selection of a folding machine conveyor belt 17 or 18. Atcontacts 97, it transfers the laundry input from the jam-med foldingmachine belt to the other non-jammed machine belt. Contacts 98 open toremove electrical power from the motor 15 and thereby stopthe jammedfolding machine. The contacts 99 close to give an alarm which could beto light (or turn off) a lamp 100.

Maintenance personnel respond to the alarm and remove the jammed laundryfrom the machine. Then, the pushbutton 95 and 101 is pushed. Theinterruption of current at 95 turns off the previously latched SCR 96and releases the relay 90. The closing of contacts 101 discharges thecapacitor 60. The circuit is now normal.

If the power is removed, the charge on the capacitor 60 leaks offthrough the diode 105. This diode is poled with a reverse bias polarity.Thus, the capacitor 60 can only discharge through the diode 105 at thevery slow rate allowed by the extremely low, reverse bias, leakagecurrent. Therefore, the riode has no real effect as long as the machinecontinues to operate.

- While the foregoing description has referred to laundry machines, theinvention will find utility wherever it is necessary to monitor a flowof input and output signals. Those skilled in the art wiil readilyperceive many needs for such monitoring. Hence, the attached claims areto be construed broadly enough to cover all equivalents reasonablyincluded within the true spirit of the invention.

I claim:

1. An automatic machine comprising a conveyor system for transportingwork pieces, said system having an input and a plurality of outputs,means for directing the flow of said work pieces from said input to aparticular one of said outputs, means for detecting jam conditionsduring which said work pieces ceases to flow to one of said outputs, andmeans responsive to said detection for giving an alarm and transferringsaid flow of said work pieces to another of said outputs.

2. The machine of claim 1 wherein said work pieces are pieces of laundryand said conveyor system transports said pieces of laundry through afolding machine.

3. A jam warning system for monitoring the flow of Work pieces through amachine, means responsive to an entrance of a work piece into saidmachine for storing a memory of said entrance, means responsive to anexit of a work piece from said machine for canceling said memory, alarmmeans responsive to the memory storage of the entrance of apredetermined number of said work pieces without an exit of any piecesfor giving an alarm, and means responsive to said alarm means fortransferring said flow of work pieces from said machine to anothermachine.

4. An automatic laundry system comprising means for conveying pieces oflaundry through a folding machine to a stacker, means for monitoring theflow of traffic through said conveyor, memory means for storing a memoryof each piece of laundry entering said conveyor, and for canceling thestorage of said memory responsive to each piece of laundry leaving saidmachine, said memory means comprising a capacitor, gate means forapplying a pulse to said capacitor responsive to the entry of each ofsaid pieces of laundry on said conveyor, means responsive to each exitof a piece of said laundry from said conveyor for discharging saidcapacitor, and means responsive to the storage of a predetermined numberof pulses on said capacitor for giving said jam warning.

5. The system of claim 4 wherein said discharging means comprises amonostable circuit triggered by said exit of said piece of laundry, andan electronic switch in series with a current limiting device, saidseries circuit being connected across said capacitor, means responsiveto the triggering of said monostable circuit for turning on said switchfor the unstable period of said monostable circuit.

6. The system of claim 5 and means for adjusting the potential stored onsaid capacitor responsive to each of said pulses to select the number ofpieces of laundry required to be in said machine simultaneously to givesaid jam warning.

7. A jam warning system comprising means for monitoring the flow of workpieces passing through an automatically fed machine, means responsive toeach entrance of a work piece into said machine for storing a memory ofsaid entrance, said memory means comprises a capacitor and a gate meansfor applying a voltage pulse having a predetermined volt-secondcharacteristic to said capacitor responsive to the entry of each of saidwork pieces into said machine, means responsive to each exit of a workpiece from said machine for triggering a monostable timing circuit, anelectronic switch controlled by said monostable circuit and connected inseries with a current limiter, said series circuit being connectedacross said capacitor, the circuit values being such that the triggeringof said monostable circuit drains a charge having said volt-secondcharacteristic from said capacitor, and alarm means operated responsiveto the storage of predetermined number of said voltage pulses without anexit of any work pieces for giving an alarm.

8. The system of claim 7 and means responsive to said alarm means fortransferring said flow of work pieces from said machine to anothermachine.

9. A monitor circuit for observing the flow of trafiic through anautomatic machine, means for storing a memory of each piece of trafilcentering said observed flow, said memory means comprises a capacitor,gate means for applying a pulse of a predetermined characteristic tosaid capacitor responsive to the entry of each of said pieces of trafiicinto said observed flow, means responsive to each piece of traificleaving said observed flow for partially discharging said capacitor tocancel the storage of one of said pulses on said capacitor, and meansresponsive to the storage of a predetermined voltage on said capacitorfor giving an alarm signal.

10. The system of claim 9 wherein said discharging means comprises amonostable circuit triggered by said piece of traflic leaving saidobserved flow, and an electronic switch in series with a currentlimiting device, said series being connected across said capacitor, andmeans responsive to the triggering of said monostable circuit forturning on said switch for the unstable period of said monostablecircuit.

11. The system of claim 10 wherein said alarm means comprises a siliconcontrolled switch connected to fire and latch when the voltage on saidcapacitor reaches a predetermined level.

12. The system of claim 11 and means for manually unlatching said switchto cancel said alarm signal.

References Cited FOREIGN PATENTS 764,607 6/1954 England.

NEIL C. READ, Primary Examiner. D. L. TRAFTON, Assistant Examiner.

3. A JAM WARNING SYSTEM FOR MONITORING THE FLOW OF WORK PIECES THROUGH AMACHINE, MEANS RESPONSIVE TO AN ENTRANCE OF A WORK PIECE INTO SAIDMACHINE FOR STORING A MEMORY OF SAID ENTRANCE, MEANS RESPONSIVE TO ANEXIT OF A WORK PIECE FROM SAID MACHINE FOR CANCELING SAID MEMORY, ALARMMEANS RESPONSIVE TO THE MEMORY STORAGE OF THE ENTRANCE OF APREDETERMINED NUMBER OF SAID WORK PIECES WITHOUT AN EXIT OF ANY PIECESFOR GIVING AN ALARM, AND MEANS RESPONSIVE TO SAID ALARM MEANS FORTRANSFERRING SAID FLOW OF WORK PIECES FROM SAID MACHINE TO ANOTHERMACHINE.